class Solution {
public:
    int takeAttendance(vector<int>& records) {
        int left=0,right=records.size()-1;
        while(left<right)
        {
            int mid=left+(right-left)/2;
            if(mid==records[mid])left=mid+1;
            else right=mid;
        }
        if(left==records[left])return left+1;
        return left;
    }
};
